The invention relates generally to a screwed connection for threaded rods which is suitable in particular for sleeve connections and end anchorages of reinforcing rods.
About thirty years ago a new connection system for concrete reinforcing rods was put onto the market under the name GEWI.RTM. sleeve connection or DYWIDAG.RTM. system. A multi-rib reinforcing rod, on which the ribs are rolled in the form of a thread over the full rod length, is used in this connection system. A screwed sleeve connection can be made with a suitably designed threaded sleeve between two GEWI.RTM. reinforcing rods cut to length as required.
However, the external thread hot-rolled on to the reinforcing rod can be produced only with relatively rough tolerances. It follows that the sleeve connection is subject to significant axial slip under load. DIN 1045 specifies that the deformation of a screwed sleeve connection (slip at both sleeve ends) under service load occurring in addition to the elastic strain may be at most 0.1 mm.
According to the DYWIDAG.RTM. system the required slip limitation is achieved by locking the threaded sleeve at each end by a lock nut. The two lock nuts are tightened by a torque wrench with a locking torque specified as a function of the nominal diameter, so that the screwed connection is prestressed with a predetermined force. Such lock nuts are used in a DYWIDAG.RTM. sleeve connection with tensile load or with combined tensile and compressive load. The two lock nuts can be dispensed with in a sleeve connection with exclusive compressive load. The end faces of the two rod ends are then braced against each other in the sleeve, so that the compressive forces are transmitted directly from rod end to rod end.
The two lock nuts increase the cost of the DYWIDAG.RTM. screwed sleeve connection and also make it more difficult to produce. In fact the lock nuts are not always easily accessible for the torque wrench, and the torques to be produced are already 950 Nm for a nominal diameter of 28 mm, i.e. at the strength limit of an average worker.
To save the two lock nuts in a screwed sleeve connection WO 98/10158 suggests to eliminate the thread play by pouring cement slurry into the screwed-on threaded sleeve. However, this method is relatively unreliable compared to the DYWIDAG.RTM. system with lock nuts. For example, it is not ensured that the thread play is always satisfactorily filled on the construction site.
There is a long felt need for a screwed connection between a rod end with a coarse external thread and a threaded sleeve, which is screwed on to the external thread of the rod end, in which the axial slip caused by the rough tolerances of the outer thread is reduced in an inexpensive and simple, but reliable manner.